The norovirus is a single-stranded (plus strand) RNA virus that belongs to Caliciviridae norovirus, that has a diameter of approximately 30 nm, and that has no envelope. The norovirus was first identified as a pathogen responsible for food poisoning and acute gastroenteritis in the U.S.A. in 1963 and since then has been detected worldwide. In food poisoning cases caused by the norovirus in the past six years in Japan, the annual incidence of food poisoning cases is approximately 270 (approximately 18% of the total number of food poisoning cases), and the annual number of patients is approximately 10,000 (approximately 30% of the total number of victims of food poisoning). Sources of primary infection include food materials, for example, bivalves, such as oysters, and sources of secondary infection include vomit and excrement of patients. In particular, secondary infection is greatly responsible for the spread of infection. The norovirus is highly infectious; 10 or more viral particles are believed to be sufficient for infection.
A vaccine or a therapeutic agent for the norovirus has not yet been developed, and the only measure against norovirus infection is to heat high-risk foods and disinfect cooking utensils and hands. However, benzalkonium chloride and ethanol presently used as antimicrobial agents for various purposes in places for cooking and processing food, such as eating establishments, facilities providing meals, and factories, have no recognized efficacy against the norovirus. Chlorine bleach (such as sodium hypochlorite), iodine preparations (such as povidone-iodine), and aldehyde agents (such as glutaral) are believed to be efficacious to some extent. However, taking the safety of the human body into account, application of these agents to fingers of workers and cooking utensils is not appropriate, not to mention the direct application of these agents to food.
Against this backdrop, there is a strong demand for an anti-norovirus detergent and disinfectant that can keep fingers of workers and cooking utensils hygienic in a safe way. However, few components that have a high antiseptic effect on the norovirus and are safe for the human body have been found, and such an ideal detergent has not been developed. By way of limited example, JP 2007-045732 A (Patent Literature 1) discloses a disinfectant solution that has norovirus-inactivating activity and that clearly is safe and mild on the skin. The disinfectant solution contains 0.05% to 0.5% by weight polyhexamethylene biguanide compound, preferably further contains 40% to 80% by weight alcohol, and has a pH in the range of 9 to 12.
“The astringent juice of the persimmon” produced by fermenting an extract from a persimmon has been used as Chinese herbal medicine, such as an antihypertensive, in China for a long time and is also familiar to Japanese as folk medicine. The astringent juice of the persimmon is rich in tannin and is believed to have astringency (the property of contracting a tissue by combining to a protein or another substance), antimicrobial action, and deodorizing action. Utilizing this functionality, for example, JP 2005-232043 A (Patent Literature 2) discloses an antimicrobial dental composition that contains an extract from the astringent juice of the persimmon, the extract being covered with cyclodextrin to improve its handleability and antimicrobial properties, and JP 2001-172861 A (Patent Literature 3) discloses a textile product in which fibers impregnated with a solution containing a functional agent (such as a deodorant or an antimicrobial agent) and the astringent juice of the persimmon or persimmon tannin are bound utilizing the stypsis of persimmon tannin.
JP 2006-206558 A (Patent Literature 4) discloses an antimicrobial composition that contains a tannin substance, a fatty acid ester, and a chelating agent (Claim 1). Examples of the tannin substance include tannic acid, pyrocatechol, gallic acid, persimmon tannin, tea tannin, and gall tannin (Claim 4). However, the efficacy of the antimicrobial composition is demonstrated only for tannic acid in Escherichia coli and Staphylococcus aureus (Examples), and Patent Literature 4 does not specifically disclose a technical idea that only persimmon tannin of the tannin substances has marked anti-norovirus characteristics and that persimmon tannin is a very important component of an anti-norovirus composition.
The structure and a purification method of tannin contained in Diospyros kaki (condensed tannin) can be found in the following two papers (Matsuo and Itoo, 1981a/1981b: Non-patent Literatures 1 and 2).    [Patent Literature 1] JP 2007-045732 A    [Patent Literature 2] JP 2005-232043 A    [Patent Literature 3] JP 2001-172861 A    [Patent Literature 4] JP 2006-206558 A    [Non-patent Literature 1] MATSUO, Tomoaki and ITOO, Saburo (1981a): Comparative Studies of Condensed Tannins from Several Young Fruits. J. Japan. Soc. Hort. Sci., 50(2), 262-269.    [Non-patent Literature 2] MATSUO, Tomoaki and ITOO, Saburo (1981b): A Simple and Rapid Purification Method of Condensed Tannins from Several Young Fruits. Agric. Biol. Chem., 45(8), 1885-1887.
It is an object of the present invention to provide an anti-norovirus agent that has high norovirus-inactivating activity and is safe for the human body, and an anti-norovirus composition that contains the anti-norovirus agent and is useful for disinfection and infection control against the norovirus.